1. Field of the Invention
The present invention relates to a method for applying a viscous material such as a sealing agent to a for liquid crystal panel, or for applying a resistance material, conductive paste, and the like to a printed wiring circuit.
2. Description of the Prior Art
Conventionally, a printed circuit has been formed using methods of photogravure printing, screen printing, etc. In rare cases, a partial circuit has been formed on a substrate by the employment of a dispenser. However, when a coating is applied in a thickness of microns, particularly, in the case of printing a liquid crystal or the like, adhesion of dust to the film has to always be taken into consideration.
FIGS. 11, 12(a) and 12(b) are views of conventional coating methods. FIG. 11 shows the screen printing, method wherein an application material or a coating material (59) is placed on a screen (57) having a predetermined pattern formed thereon, and a squeegee (56) is moved in a direction shown by an arrow, so that the object (58) is coated with a film (61).
When both a thermohardening resinous adhesive agent and an ultra-violet ray hardening adhesive agent are used together as a sealant for a liquid crystal panel, or when a resistance member and an insulative member are simultaneously formed on a circuit board, it is required that the two kinds of viscous materials be coated without any interval therebetween. In such cases as described above, however, an earlier-coated film should be hardened or sintered before a second film is applied by the screen printing method in order to avoid stains of the earlier-coated film resulting from contact with the screen. Therefore, in the conventional screen printing method the number of processes including the hardening process and the sintering process cannot be sufficiently reduced.
Furthermore, the screen printing method has drawbacks, in that not only is dust adhered to the surface of the screen, but traces of mesh are marked on the surface of the printed film because of repeated use of the screen. Therefore, it has been difficult to achieve a coating of a uniform thickness and a smooth surface using the screen printing method.
On the other hand, FIGS. 12(a) and 12(b) shows a conventional coating method which uses a dispenser. After a substrate (64) is coated with a coating material (63) through a nozzle (62) as shown in FIG. 12(a), the surface is further coated with a coating material (66) by a different dispenser. (65) as shown in FIG. 12(b). Therefore, this method represented in FIGS. 12(a) and 12(b) requires twice the coating processes. In addition, in the above-described dispenser coating method, the nozzle may come into contact with the substrate during the second coating process, resulting in the need for a high degree of positioning accuracy.
It is known to be desirable that the preferable mode of applying sealing agents to a liquid crystal is for the sealing agents which have their own characteristic functions to be coated in many rows such as the double-structured sealing agent disclosed in Japanese Patent Laid-open Publication Tokkaisho No. 60-69634 (69634/1985), from the viewpoint of the affinity with the liquid crystal, ratio of humid permability, etc. However, when a dispenser is used for applying the coating of the sealing agents as disclosed in Japanese Patent Laid-open Publication Tokkaisho No. 60-179722 (179722/1985), the earlier-coated sealing agent usually comes into contact with the dispenser, because the coating process is carried out twice, resulting in an insufficient sealing structure of the liquid crystal. Further, when the present inventors tried to form a temporary hardening sealing agent by the use of the dispenser after coating of the sealing agent as disclosed in Japanese Patent Laid-open Publication Tokkaisho No. 60-119526 (119526/1985), they found it difficult to adjust the position of the temporary hardening agent with that of the earlier-coated sealing agent. Moreover, they also found it difficult to coat the temporary hardening agent at the same distance from the substrate as that of the earlier-coated agent.